Overview

Much of the early literature describes the properties of Nafion . More recently, reliable information about the new Hyflon-Ion polymer has become available [5,9]. This polymer is based on the same monomer as the experimental Dow polymer, which has been discontinued.

The comparison of ionomers of different length of the side chain is somewhat difficult. In the literature, this comparison is usually made on the basis of equal equivalent weight (EW). This is neither entirely reasonable nor practical, as can be seen by the Nafion-Dow comparison: It assumes that removing 166 weight units from the branches (166 is the weight of the extra HFPO unit in Nafion) and replacing it with 1.66 extra polytetrafluoroethylene (pTFE) units in the backbone should have no effect on the properties. This of course is not true. If the comparison is done on the basis of identical comonomer ratios, then the EW scale is displaced by 166 units (1046 EW Nafion would be compared to 880 EW Dow polymer). This comparison assumes that the extra hexafluoro propylene epoxide (HFPO) unit in the branch should not affect the properties of the polymer. This is also not the case; the extra HFPO unit decreases crystallinity, enhances the formation of ionic clusters and in general "plasticizes" the polymer similar to the effect of additional comonomer. From an empirical standpoint, a displacement of about 240 EW units (1046 EW Nafion compared to 806 EW Dow) would put the two polymers on a comparable basis. On...